The present invention relates generally to ion exchange membrane electrolytic process of brine such as solution of sodium chloride, and more specifically to an electrolytic process that is capable of electrolysis with high efficiency even when run at decreased brine concentrations.
For ion exchange membrane electrolysis of brine, each member of an ion exchange membrane electrolyzer is designed such that the electrolytic process can be run with high current efficiency while the electrical energy taken for electrolysis remains decreased, and the concentration, temperature, etc. of brine fed to the anode chamber of the ion exchange membrane electrolyzer are determined in such a way as to achieve efficient electrolysis.
As set forth typically in GB14080538, it has also been proposed to run an ion exchange membrane electrolyzer while the pressure of a cathode chamber is higher than that of an anode chamber to bring a cation exchange membrane in close contact with an anode, thereby efficiently running the electrolyzer at a decreased cell voltage. In a commercially available ion exchange membrane electrolyzer, it has been proposed to place a cation exchange membrane in close contact with an anode or reduce the gap between the cation exchange membrane and the anode and cathode down to substantially zero.
In an electrolytic system comprising ion exchange membrane electrolyzers, not only the ion exchange membrane electrolyzers but also associated setups including a brine feeder have capabilities of running the ion exchange electrolyzers with optimum efficiencies.
The need of increasing outputs may possibly be met by increasing the number of ion exchange membrane electrolyzers; in consideration of the capability of a brine feeder, however, it is commonly difficult to feed brine in the same concentration and flow rate as before to each ion exchange membrane electrolyzer from an existing brine feeder setup.
As the electrolytic system is run using the existing brine feeder setup while the amount of brine fed to each ion exchange membrane electrolyzer is decreased, there is a decrease in the concentration of dilute brine taken out of the ion exchange membrane, which otherwise causes more electroosmosis water to pass from an anode chamber into a cathode chamber, resulting in considerable decreases in current efficiency.
It has also been proposed to use an improved ion exchange electrolytic process wherein the concentration of brine fed to an anode chamber is adjusted to control the amount of electroosmosis water passing toward a cathode chamber side, thereby producing an aqueous sodium hydroxide solution having a desired concentration without substantially adding water to the cathode chamber (U.S. Pat. No. 3,773,634). However, the ensuing current efficiency is 41% to 80%, figures that are quite worthless for practical ion exchange membrane electrolysis.
In electrolysis, decreased current efficiency is a negative factor of vital significance; it is considered impossible to run an ion exchange membrane electrolyzer assembly while there is more electroosmosis water, and so never until now has it been proposed to increase the number of ion exchange membrane electrolyzers without enhancing the capability of the brine feeder setup.
A primary object of the invention is to provide an electrolytic process using an ion exchange membrane electrolyzer assembly, which enables efficient electrolysis without any current efficiency drop, even when decreases in the concentration of brine fed to the ion exchange membrane electrolyzer assembly cause more electroosmosis water to occur in an existing electrolytic arrangement wherein more ion exchange membrane electrolyzers are used without enhancing the capability of a brine feeder setup.